A ferromagnetic hybrid Weyl semimetal in two dimensions: the monolayer AgCrS2

Topological quantum phases in two-dimensional materials have been a fascinating research topic since the discovery of graphene. Particularly, the topological quantum phases could appear in two-dimensional magnetic systems. However, identifying concrete materials that host topological quantum phases is still a challenge, especially the magnetic ones. In this work, we propose a novel hybrid Weyl semimetal in two dimensions, the monolayer AgCrS2. We show that this material has a stable ferromagnetic ground state with an in-plane magnetic moment. Particularly, it hosts a hybrid of two Weyl nodes close to the Fermi level: one is a double Weyl point, and the other one is type-II linear Weyl point. The features of their band structure could be inferred from the effective models for them. When the spin-orbital coupling is included, the double Weyl point is gapped. In comparison, the type-II linear Weyl nodes on high-symmetry path can be tuned by controlling the orientation of the magnetization direction. To be specific, the magnetization could change locations of type-II linear Weyl nodes and control its stability. Therefore, our results offer a platform to study novel hybrid of Weyl nodes in two-dimensional ferromagnetic system.